Wikipedia:Reference desk/Archives/Computing/2011 December 10

= December 10 =

Adaptive 3D Y / C Comb Filter
What is a Adaptive 3D Y / C Comb Filter on a television? 184.7.157.90 (talk) 02:24, 10 December 2011 (UTC)
 * Have you had a look at comb filter? See also dot crawl for the problem it's intended to fix.  For more info, see .  Do you need to know the mathematics or electronics, or do you just want the high-level overview for keen TV watchers? --Colapeninsula (talk) 16:28, 12 December 2011 (UTC)

scanning objects on a flatbed scanner
Can I scan flowers or leaves on a flatbed scanner without damaging it? --117.253.191.91 (talk) 13:51, 10 December 2011 (UTC)


 * I would probably prop the lid up a bit with something else (e.g. a small book), so it wasn't in contact with the flowers/leaves. --Mr.98 (talk) 14:06, 10 December 2011 (UTC)


 * Why do you want to scan them? I ask because there may be a better way to accomplish whatever it is that you want to do.  Dismas |(talk) 14:40, 10 December 2011 (UTC)


 * To answer your question, you are unlikely to damage the scanner, although the glass would need careful cleaning afterwards. However, a scanner is designed to photograph flat objects only.--Shantavira|feed me 14:45, 10 December 2011 (UTC)


 * The Scanography article discusses what people have found possible, and the limitations of (mis)using a scanner in this way. -- Finlay McWalterჷTalk 14:58, 10 December 2011 (UTC)


 * This article shows some unorthodox scans of things like leaves and shrimp. -- Finlay McWalterჷTalk 15:08, 10 December 2011 (UTC)

Network layers
Im doing a networking course and we were analysing packets and one of the packets had an ICMP packet embedded within an IP packet (or the other way round; not important for what I'm asking). My question is how can this be if they are both at the network layer? Shouldn't it be one per layer? --178.208.219.151 (talk) 16:17, 10 December 2011 (UTC)


 * ICMP packets are encapsulated in IP packets; as the ICMP article says "Although ICMP messages are contained within standard IP datagrams, ICMP messages are usually processed as a special case". It sounds like you're trying to interpret the TCP/IP hierarchy in terms of the 7 layer OSI model, but there isn't a perfect mapping between the two - as the latter article says "In the TCP/IP model of the Internet, protocols are deliberately not as rigidly designed into strict layers as in the OSI model". So ICMP is a network layer protocol wrapped in another network layer protocol, but not necessarily handled in the say way that other packets in the wrapping network layer are handled. -- Finlay McWalterჷTalk 17:29, 10 December 2011 (UTC)

Web site opening trouble
Why some websites do not get opened in my home computer, whereas they are easily opened in my office computer?For example the URL of the site is www.jpl.nasa.gov. — Preceding unsigned comment added by 49.244.103.175 (talk) 18:08, 10 December 2011 (UTC)


 * Could be to do with your bandwidth. If you've got a slow connection at home, some content heavy pages may not load properly (and jpl's probably got a lot of content), but on a faster connection at work they could load no problems. I have seen this problem on many occasions without the browser actually reporting an error. Another possibility is that your browser software is out of date at home, and pages optimised for current browsers may not display on an older browser. You may even be using totally different browsers at home and work; while this isn't usually a problem these days, some sites won't display properly, if at all, in some browsers. Additionally you could be missing required plugins at home; the jpl site for example requires some browser plugins. --jjron (talk) 03:38, 12 December 2011 (UTC)

Why do browsers not tend to render text first?
Often it is observed that web browsers do not render text first while loading a web page, as the webpage is getting loaded. This is more pronounced when accessing pages through a slow internet connection, when the text may appear much later after the user has started loading a web page. Is this a valid observation, if so what are the possible reasons for this behaviour. Gulielmus estavius (talk) 19:49, 10 December 2011 (UTC)


 * First the browser loads the html. Then it parses that, and recovers a list of assets it needs to download (images, stylesheets, javascript, more html, fonts). These it adds to a workpile which is watched by asynchronous download threads, which set off downloading those. I take your question to mean that at this point, when it has the HTML but not the assets, why doesn't it immediately render the text of the page?  It certainly could.  The trouble is that it doesn't really know how soon those other assets will be available (they come from different servers and may come almost immediately, in a long time, or never). Imagine the browser took an aggressive policy, where it rendered the page as soon as it could and then re-rendered it each time it loaded an asset that materially changed the layout. On a fast site (where the assets load quickly) the page would be recalculated and rerendered a dozen or two times in the first few seconds of you looking at it; that would be exceptionally annoying, and could lead you to clicking links you hadn't intended (you're clicking on one link, but the page reformats while you do so, and you end up clicking on the wrong thing). Alternatively the browser could take a very passive approach, and not lay out until all the assets were available - that's really bad too, because a single slow asset means the whole page is blank, potentially for a minute (or however long until the browser gives up).  So a compromise has to be found.  The browser authors would really like to draw the page just once, like turning on a TV set,  so they put a timeout at the beginning, and don't render anything until that expires (or all the assets are present). For a fast site the page just works.  But for a slower one, where that timeout expires, they have to give up and render what they can (to give the user the idea that something is actually happening).    Thenceforth they probably chunk updates again, again to avoid a flutter of annoying redraws, before again flushing out the changes they can show.  Different browsers will have different schemes for waiting and flushing, and there's no right way to do it. -- Finlay McWalterჷTalk 20:17, 10 December 2011 (UTC)


 * Some browsers also decide if they have enough info to layout the page properly they draw it. They can do this if the information in an as-yet-unloaded asset (particularly an image) wouldn't affect the layout. So explicitly specifying the sizes of things (particularly images) in HTML or CSS can give the browser all the info it needs.  If the page doesn't, the browser needs to load the image to know its size (strictly it needs to load the start of the image, but it's rare to peek at a partially loaded asset) or the sizes of boxes that contain it or would be shunted around by its changing size, then the browser can't know how to accurately lay the page out. -- Finlay McWalterჷTalk 20:23, 10 December 2011 (UTC)

vandals
I dont know if this is the right place to ask, but what is the most vandalize page in wikipedia? Mah Ad ik usap 21:37, 10 December 2011 (UTC)


 * Pls. Cancel Mah Ad ik  usap 21:44, 10 December 2011 (UTC)

"TCB" and "SYN-RCVD state"?
Been reading RFC 1948 and in the "A common TCP bug" section it says "When SYN packets are received for a connection, the receiving system creates a new TCB in SYN-RCVD state." So what do "TCB" and "SYN-RCVD state" mean? I have no idea what TCB is. I imagine SYN-RCVD stands for SYN received but what is it exactly? A state of what? --178.208.219.151 (talk) 22:14, 10 December 2011 (UTC)


 * SYN-RCVD (fully SYN RECEIVED) is explained at Transmission Control Protocol, and also see the state transition diagram in this section. -- Finlay McWalterჷTalk 23:16, 10 December 2011 (UTC)


 * A TCB is a Transmission Control Block, and is described here; roughly speaking its a single entry in a little table that a TCP stack has to maintain to keep track of all the simultaneous connections it's handling. -- Finlay McWalterჷTalk 23:21, 10 December 2011 (UTC)